<sect2 id="calc-apcoords">
<title>Apparent Coordinates module</title>
<indexterm><primary>Tools</primary>
<secondary>Astrocalculator</secondary>
<tertiary>Apparent Coordinates module</tertiary>
</indexterm>

<screenshot>
<screeninfo>The Apparent Coordinates calculator module </screeninfo>
<mediaobject>
  <imageobject>
    <imagedata fileref="calc-apcoords.png" format="PNG"/>
  </imageobject>
  <textobject>
    <phrase>Apparent Coordinates</phrase>
  </textobject>
</mediaobject>
</screenshot>

<para>The Apparent Coordinates module converts the <firstterm>catalogue coordinates</firstterm> of a point in the sky to its <firstterm>apparent coordinates</firstterm> for any date. The coordinates of objects in the sky are not fixed, because of <link linkend="ai-precession">precession</link>, nutation and aberration. This module takes these effects into account. </para>
<para>To use the module, first enter the desired target date and time in the <guilabel>Target Time/Date</guilabel> section. Then, enter the catalogue coordinates in the <guilabel>Catalog Coordinates</guilabel> section. You can also specify the catalogue's epoch here (usually 2000.0 for modern object catalogues). Finally, press the <guibutton>Compute</guibutton> button, and the object's coordinates for the target date will be displayed in the <guilabel>Apparent Coordinates</guilabel> section. </para>
</sect2>
